We are truly sorry to hear that you are dealing with such a troubling situation. Firstly, it is important to understand that witchcraft and any form of sorcery is strongly condemned in the Bible. As it is written in Galatians 5:19-21 WEB, "Now the works of the flesh are obvious, which are: adultery, sexual immorality, uncleanness, lustfulness, idolatry, sorcery, hatred, strife, jealousies, outbursts of anger, rivalries, divisions, heresies, envyings, murders, drunkenness, orgies, and things like these; of which I forewarn you, even as I also forewarned you, that those who practice such things will not inherit the Kingdom of God." In Deuteronomy 18:10-12 WEB, "There shall not be found with you anyone who makes his son or his daughter to pass through the fire, one who uses divination, one who practices sorcery, or an enchanter, or a sorcerer, or a charmer, or a consulter with a familiar spirit, or a wizard, or a necromancer. For whoever does these things is an abomination to Yahweh".
We must also discuss adultery and sexual immorality if this is relevant to the relationship with your former girlfriend. This is also considered sin according the above scripture. If sexual sin did occur, this must stop and be repented of before God.
Part of the problem may be the relationship itself. The Bible is clear that we must not be joined together with unbelievers. This includes intimate and committed relationships such as dating. In 2 Corinthians 6:14, WEB, "Don't be unequally yoked with unbelievers, for what fellowship have righteousness and iniquity? Or what fellowship has light with darkness?". Therefore, do not be involved intimately or committally with anyone that is practicing these sins.
It is important to note that the only way to be saved from these sins and their eternal consequences is through Jesus Christ. In Acts 4:12, WEB, it is written, "There is salvation in none other, for neither is there any other name under heaven, that is given among men, through which we must be saved!" Jesus is the only way. If Jesus is not mentioned in your requests then we encourage prayer through the saving name of Jesus.
Let us pray together for your protection and deliverance in Jesus' name."Father in heaven, we come before you in the mighty name of Jesus. We pray for your protection over this individual and we rebuke any form of witchcraft or sorcery that may be directed towards them. We ask that you sever any ungodly soul ties that may exist between them and their former girlfriend, and we pray that you surround them with your hedge of protection. We also pray for their former girlfriend, that she may come to know the truth of the Gospel and be set free from the bondage of sin according to John 8:36, WEB.